Eighteen-year-old Kyle Best was driving his pickup on a New Jersey road in 2009 when he crossed a double yellow line and sideswiped a motorcycle. The married couple he hit, Linda and David Kubert, each lost part of a leg.

Best was texting moments before the accident. The Kuberts sued not only Best, but also Shannon Colonna, a 17 year-old girl who had sent Best one text during his drive.

A New Jersey court held that Colonna was not liable, because there was no evidence she knew Best was driving when she texted him. That should have ended the inquiry, but two of the three judges went further and established a new legal rule for future New Jersey cases: A remote sender of text could be liable if he or she knew the recipient was driving at the time the text was sent.

This is not just bad jurisprudence  judges are not supposed to reach out and decide issues unnecessary to the case in front of them  but awful public policy.

Lets acknowledge that texting while driving is a potentially dangerous thing, if not as dangerous as, say, riding a motorcycle. Any distractions to a driver  texting, talking on a cell-phone, arguing with a car passenger, eating  can reduce reaction times or induce carelessness dangerous to the driver and others.

Still, one strongly suspects that the problems of texting are overstated: The drivers most likely to text are the same teenage drivers who are the worst drivers generally, and traffic fatalities are far lower now than 20 years ago when there was no texting at all.

Moreover, some studies have shown that draconian penalties against texting while driving seem to increase risks to public safety. The benefits from deterring some conscientious drivers from texting are more than offset from the increased danger from other drivers texting surreptitiously in their lap (to avoid getting caught texting) instead of texting above the dashboard where theyll be less distracted.

But we can agree that a driver who causes an accident while texting is negligent and should usually be held liable. The problem is extending the scope of liability to those outside the car.

Even in the worst-case scenario, where Shannon texts Kyle knowing that Kyle would carelessly respond while driving, Shannon wasnt the one who made Kyle respond to the text. That was Kyles choice. Holding the less-culpable Shannon liable, too, actually reduces the deterrence to Kyle from being held accountable for his own actions.

But most cases will not be the worst-case scenario. A parent will text a teenager, Call me when you arrive, intending the recipient to read the text at the end of the drive; friends will text one another without knowing that the other is currently driving; or the recipient might not check the text until hours later, while driving and bored.

All these people are innocent, but if their correspondent gets into an accident, theyll be sued by a lawyer seeking to prove possible liability. This would not be a problem if lawsuits were costless, but demonstrating ones innocence by summary judgment can cost tens of thousands of dollars in legal fees with no hope of recoupment. Everyones insurance rates go up. The only beneficiaries are the lawyers.

The only thing one can do to avoid the possibility of such suits is to not text anyone ever. (Of course, you might be texting someone to avoid interrupting a driver with an even more distracting phone call, but the New Jersey court didnt consider that.)

Coincidentally, Nobel-Prize winning economist Ronald Coase died this week. His groundbreaking insight was that people arrange their affairs to avoid the expense of transaction costs.

By inventing a new form of secondary liability, the New Jersey court failed to learn Coases lesson, and have increased transaction costs for all of us.

One hopes the legislature will step in to fix this disaster; one fears that the hysteria over texting while driving will lead other courts and legislatures to move in the wrong direction.